CNET News reporter Daniel Terdiman drove this Audi Q7 TDI clean diesel SUV for 5,765 miles on Road Trip 2009. Along the way, the vehicle averaged about 21 miles a gallon on the highway, not bad for a car of its size.
Daniel Terdiman/CNET

When I first began talking with Audi about road-testing the company's new Q7 TDI clean diesel SUV on Road Trip 2009, I have to admit that I was more than a little bit suspicious of that term.

"Clean diesel." It sounded a lot like another new term of art, "clean coal," and I think we know pretty well that there really isn't much that's clean about coal. Plus, I think many of us have negative associations with diesel, a technology long known for sooty fumes, loud engines, and a whole lot of pollution.

Still, Audi was talking about high fuel efficiency, low emissions, and an engine that rivaled--or even surpassed--the power of its traditional gasoline counterparts. Indeed, there was even the discussion about outdoing hybrids for overall performance in certain driving conditions.

Since this would be a vehicle I knew I would be driving for more than 5,000 miles, I began to do a little research. Before I signed on, I wanted to have a sense that I wouldn't be one of those drivers leaving dark clouds of exhaust all over America's highways, and that the Q7 wouldn't eat up my budget at the fuel pump.

Among the very first items I found online was a 2008 Popular Mechanics article by Ben Hewitt exploring clean diesel and whether it truly is clean in any real sense of the word.

The article's opening paragraph certainly seemed to say that it was:

"Merging with northbound traffic on Interstate 75 just outside Auburn Hills, Mich., I punch the accelerator, quickly swing left into the passing lane and pull forcefully ahead of the cars around me," Hewitt wrote. "In any other ride, on any other gray morning, it'd be just another Interstate moment. But this rush hour, I'm behind the wheel of a preproduction 2009 Volkswagen Jetta, which is powered by a 2.0-liter turbo-charged, direct-injected diesel engine that, even as I leave the speed limit in tatters, is averaging nearly 50 mpg. Equally important, what's coming out of the tailpipe is no dirtier than the emissions from the 35-mpg econoboxes I can now see in my rearview mirror. Speed, fuel efficiency and minimal emissions? These aren't characteristics usually associated with diesel-powered vehicles. But they will be."

I tend to trust Popular Mechanics as merchants of sober journalism, so after reading Hewitt's piece lauding the coming of clean diesel, I decided it was worth trying the Q7 TDI out. After all, I thought, it looked like a pretty spiffy car, and one that might well even get better gas mileage than my own Subaru Outback.

Of course, I wanted to hear from Audi itself why they thought clean diesel was a technology to be reckoned with. So I asked the company a number of questions about it, including what, in fact, makes it "clean?"

According to Brad Stertz, Audi of America's corporate communications manager, there are two main reasons, the first being the adoption across the United States of a new, ultra-low-sulfur diesel fuel.

"Cleaner fuel has allowed further advancements in the Audi TDI engine," Stertz said in a written response to my questions. "The injection system, with its maximum injection pressure of 2000 bar, an all-round advanced exhaust gas recirculation system and an optimized turbocharging system are at the heart of this evolution. A new feature is the integrated cylinder pressure control. All of these things have combined to ensure each drop of diesel fuel burns more efficiently during combustion, thereby reducing emissions and improving fuel economy. (Each drop of diesel gets 12% more power than a drop of gasoline and that translates into 25-30% better fuel efficiency.) All of these modifications constituted the first step in radically reducing the engine's raw emissions."

Further, he said, the TDI engine significantly reduces nitric oxide emissions through the use of a DeNOx converter, "which dramatically eliminated nitrous oxide, a leading factor in smog."

In the end, he said, "the ultra low emission system allows emissions to be minimized by combining modifications inside the engine with an innovative exhaust gas after-treatment system. The result is reduced fuel consumption and the world's cleanest diesel engine."

Picking up the Q7 On June 20, I picked up the Q7 TDI in Denver. It was an exciting moment since, as you can probably gather, there's no Road Trip without a vehicle. And I knew I'd be in this car for several thousand miles.

The Audi Q7 TDI that CNET News reporter Daniel Terdman drove during Road Trip 2009, as seen through one of the concrete tubes that make up artist Nancy Holt's great Earthwork, the Sun Tunnels.
Daniel Terdiman/CNET

For the first few days, I didn't try much of anything requiring me to change any settings or do much beyond accelerating and braking. I was too caught up in trying to get the trip going and adapting to its pace. Not to mention the high-altitude I instantly encountered in Colorado. In fact, within a day of my arrival, I had already gone from a mile high--Denver--to more than 14,000 feet high on Colorado's Mt. Evans.

I was certainly feeling the effects of the altitude, but the Q7, not so much. It prowled its way smoothly to the top of what is North America's highest paved road without so much as a sputter. I guess it's that Alpine heritage.

Driving it later on more traditional highways, my first impression was that the Q7 was quite powerful, and indeed, with its quiet engine, I often found myself traveling more than 90 miles an hour without any obvious sign that I was going so fast. I suppose I should have used cruise control to prevent such moments, but I never did. I preferred to control the vehicle with my foot.

In fact, I wasn't driving for speed, but when I needed it, it was there. Passing slow drivers was where I'd say the Q7 really shined: time and again, I would fly by folks with no apparent effort. I'd simply step on the accelerator, and off we'd go.

Fuel efficiency In the literature I'd read about the Q7 TDI, I found that its 225 horsepower, 406 lbs. ft of torque, 3.0 liter V6 TDI clean diesel engine with a six-speed Tiptronic automatic transmission, and all-wheel drive, was capable of more than 25 miles per gallon, at least in highway driving. One reviewer even wrote about achieving 30.2 miles per gallon over 1,000 miles.

My performance, over the nearly 5,800 miles I drove the Q7, was not quite as impressive. I got about 21 miles a gallon on the highway, and somewhat less than that, probably in the 17-to-18 mpg range in urban conditions. Fortunately, I was mostly on highways.

Although it only reads 1,765 miles, this is actually the final odometer reading for Road Trip 2009, a full 5,765.4 miles of driving in Audi's Q7 TDI clean diesel SUV.
Daniel Terdiman/CNET

Still, I was a little surprised at first about getting just 21 mpg on the open road. But I think the reason is that I generally had the air conditioning on, and truth be told, was probably driving a little faster than I should have been. On the other hand, 21 miles per gallon for a vehicle the size of the Q7 is actually rather impressive. My Subaru, a much smaller car, gets 24 on the highway.

And, with a nice, big, gas tank, the Q7 would tend to get about 280 miles or so on just half a tank. That meant that while diesel turned out to be readily available everywhere I went, I never had to worry about running out of fuel.

Luxury driving As a luxury vehicle, the Q7 certainly stacks up. From the nice job Audi did of seamlessly integrating iPods and Bluetooth phones like an iPhone for safe, handsfree driving while talking on the phone or listening to music, to comfortable seating with plenty of control over seat configuration to a powerful Bang & Olufsen audio system, I pretty much always knew, getting into the Q7, that the next few hours were going to be comfortable and cushy.

It's not that I have a lot of experience with luxury cars to compare the Q7 to. Indeed, I'm certain that other high-end SUVs from manufacturers like Mercedes, BMW, Infiniti, and others, stack up quite nicely against the Q7.

Regardless, it was a pleasure to drive, a pleasure to sit in and just listen to music, escape the rain, or nap in, all of which I did during the trip.

One area where I was a little surprised was in the Q7's initial pickup. At low speeds, it seemed like the car would usually take a second or so to boost acceleration when I put the pedal to the metal. But only at low speeds since, as I wrote above, accelerating past people on the open road couldn't have been more effortless.

I did end up using the Q7's navigation system quite a bit, but I have to say that from time to time, I found it wanting. That was especially true when trying to find specific addresses or destinations in smaller towns; sometimes, the navigation system simply wouldn't acknowledge that an address even existed, and that could be quite frustrating.

But most of the time, it worked just fine, and I enjoyed having the system give me just the information I need (direction, time to arrival, and distance both to the destination and to the next turn) in a little micro-display to the left of the speedometer. Having that information available made it possible to devote the main multimedia interface to music.

On the other hand, if I wanted to be able to see a map of where I was driving, the Q7 easily showed that and a list of songs in the small display to the left. It was nice to have that choice.

Nice and spacious When packing to head out on Road Trip 2009, I had tried very hard not to bring too much stuff. One benefit of that was that the Q7 usually felt like, no matter how much I had, there was still plenty of room inside.

I didn't quite realize how much room there was until I arrived home and got in my Subaru, which, suddenly, seemed tiny. I'm sure I'll re-adapt to the smaller interior space of the Outback, but for the moment, I'm quite aware of how big the Q7 was inside.

I'm by no means a professional car reviewer, so I'm well aware that my assessment of the Q7 lacks many of the touchstones of the standard review. Regardless, I can say without reservation that my time in the Q7 TDI was thoroughly enjoyable. It's not a cheap car--the model I tested runs about $50,000--so it's far out of my personal range. But for those who have the means to swing such a transaction and who are interested in getting a vehicle that provides luxury, spaciousness, and impressive performance without sacrificing fuel efficiency, I have no qualms recommending the Q7 TDI.

In fact, I wonder if it's too late for me to go back to Denver, pick it back up, and hit the road again.